Radially expanded tubular elements can be applied in numerous applications, such as in wellbore applications where hydrocarbon fluid is produced from an earth formation. For example, it has been tried to expand tubular wellbore casing in order to allow larger downhole wellbore diameters to be achieved compared to conventional wellbore construction wherein a plurality of casings are arranged in a nested drilling procedure whereby for each newly drilled interval a new casing is lowered through the previously drilled and cased interval(s), which new casing therefore necessarily needs to be of smaller outer diameter than the inner diameter of the previously installed casing(s). This has been improved by radially expanding the new casing after having been lowered through the previously installed casing(s), whereby the new casing deforms plastically. The expanded casing allows passage therethrough of a larger diameter drill bit so that the wellbore can be further drilled at a larger diameter than in the conventional situation. A further casing is then lowered through the previously installed and expanded casing, and thereafter expanded, etc.
The end portion of an expanded tubular element, such as the end portion of the pin member of a connector, has a tendency to axially shorten due to the imposed circumferential strain in the wall of the pin member. The imposed circumferential strain at the inner surface is larger than the imposed circumferential strain at the outer surface. This can be understood by considering that the circumferential strain at the inner surface is ΔD/Di and the circumferential strain at the outer surface is ΔD/Do, and that Di is smaller than Do. Here Di is the inner diameter of the pin member, Do is the outer diameter of the pin member, and ΔD is the change in diameter due to the expansion process. Since the circumferential strain at the inner surface is larger than the circumferential strain at the outer surface, the tendency to shorten is larger at the inner surface than at the outer surface leading to a tendency of the pin member to bend radially inward. At locations remote from the end of the pin member, radially inward bending does not occur in view geometrical constraints. However, the end portion of the pin member does radially bend inwardly if no corrective measures are taken. Of course, the end portion of the box member also has a tendency to bend radially inward. However, inward bending of the box member end portion is less of a problem than inward bending of the pin member as the latter phenomenon causes an internal upset of the tubular element. Hence it will be understood that such radially inward bending of the pin member is a drawback in many applications of expanded tubulars.